Packet-based network nodes, such as switches and routers, generate a database of forwarding information that is used to forward incoming packetized traffic. The forwarding information is generated through software-based protocols that are executed by a central processing unit (CPU). In order to increase the speed and throughput of switches and routers, the forwarding information is often programmed into hardware-based forwarding tables. The hardware-based forwarding tables can be rapidly searched to provide forwarding decisions without ever having to utilize the resources of the CPU. When forwarding information for a received flow of packets does not exist in the hardware-based forwarding table, the packets from the flow are sent to the CPU for processing until forwarding information can be learned and a forwarding table entry can be programmed into the hardware-based forwarding table. The CPU of a network node has a finite processing capacity and as more packets are sent to the CPU, more of the finite processing capacity is consumed by processing the received packets. If the load on the CPU is too great, the response time of the CPU will slow and some packets may be dropped.
Many of the most advanced switches and routers utilize a chassis-based distributed architecture in which separate linecards are dedicated to different functions. For example, a control module linecard is dedicated to central management and control operations, port interface linecards are dedicated to sending and receiving network traffic and performing hardware-based forwarding, and a switch fabric linecard is dedicated to providing data paths between the various linecards. In a distributed architecture, the control module includes a main CPU that is responsible for generating and managing the forwarding information for the entire network node and for programming the hardware-based forwarding tables of the port interfaces. The wide set of responsibilities of the control module makes the finite processing capacity of the main CPU a very valuable resource.
In view of the foregoing, what is needed is a technique for efficiently managing the utilization of processing resources in a packet-based network node.